Abaddon

"'Abbadon and I had almost broken out of the prison. We were on the verge of ultimate power.' -Zarek MB; UBA Unlimited, Episode I"The Great Demon-God of the Abyss, Abaddon is a creature shrouded in mystery, often considered to be one of the oldest and most malevolent beings in creation

History
The first recorded appearance of Abaddon was when he ripped through the time-space fissure in the heart of Racnoss and tore the planet apart from the inside. After this, he began moving through time and space and tearing apart planets with his bare hands for nearly 700 decades, until his reign of terror escalated with his infamous duel with the Hybrid of Evil at the Medusa Cascade, which some accounts indicate lasted several thousand years. After the end of the great duel, both were on the brink of death, and Abaddon was taken by the Disciples of the Light to a pocket dimension, where he was imprisoned and tortured for nearly 17,000 years, until directly after the First Zarek MB Conflict, when Zarek MB was cast into the same prison dimension as Abaddon. The two began to formulate a plan for Zarek MB and Abaddon to escape, which escalated into Donald Trump summoning Zarek MB, who then started the Second Zarek MB Conflict, which eventually failed. Abaddon's fate after this is unknown, as he was never summoned in and Zarek MB was killed by Zarek.